1. Field of the Invention
The present invention relates to a stereoscopic display device which provides stereoscopic images to observers with naked eyes.
2. Description of the Related Art
A naked-eye type stereoscopic display device does not require any special eyeglasses, so that the observer can enjoy stereoscopic images readily. With personal mobile terminals such as mobile phones, smartphones, and feature phones and household display devices such as television set receivers, such techniques for achieving in naked-eye type stereoscopic display are being developed rapidly.
The naked-eye type stereoscopic display techniques achieve stereoscopic display by giving directivity to the light emitted from a display and providing parallax images to each of the both eyes of an observer. Examples thereof may be a 2-viewpoint stereoscopic image display technique, a multiple-viewpoint stereoscopic image display technique, and an integral photography (IP) technique.
There are various members as a light-ray control module for giving the directivity to the emitted light. Examples thereof may be a type which utilizes a lens or a barrier on the display surface and a type in which the light emitted from the display device itself has the directivity.
A display panel is typically formed by arranging, in a matrix form, pixels each displaying a minimum element of an image. In a naked-eye type stereoscopic display device, it is necessary to display viewpoint images corresponding to the number of viewpoints. Thus, sub-pixels for displaying minimum elements of the viewpoint images are required further.
Note here that there are cases where an element having a color expressing function for displaying a color of an image is referred to as a “sub-pixel”. For example, such term is used in an expression “a pixel constituted with sub-pixels of red, green and blue”. However, if it is not specifically mentioned, the “sub-pixel” in the current Specification is defined to be an element including a viewpoint image displaying function for convenience. Note that the sub-pixel in the current Specification can also include a color expressing function.
The sub-pixel is a device for converting an electric signal into an optical signal. The region between a sub-pixel and another sub-pixel is a region where optical conversion cannot be done. When a part, which is not intended to be viewed, in that region is viewed by an observer in an expanded manner due to the light-ray control module, a sense of discomfort is given to the observer. The state of such image quality is referred to as 3D moiré.
As a countermeasure for 3D moiré, there is proposed a related technique with which an overlapping region is provided in optical aperture parts of two sub-pixels neighboring to each other in the viewpoint direction and the total values of the longitudinal aperture widths are set to be constant (Japanese Unexamined Patent Publication Hei 10-186294 (Patent Document 1)). Further, also proposed is a related technique with which the total values of the longitudinal aperture widths are set to be constant by utilizing the sub-pixels arranged over a plurality of rows (Japanese Unexamined Patent Publication 2008-249887 (Patent Document 2)). Furthermore, also proposed is a related technique with which the visibility of 3D moiré is decreased by devising the longitudinal aperture widths in the overlapping regions of the sub-pixels (Japanese Unexamined Patent Publication 2012-063556 (Patent Document 3)).
However, there is such an issue that the visibility of 3D moiré cannot be decreased sufficiently even when the above-described related techniques are used. This issue will be described in details hereinafter by using FIG. 15A to FIG. 17.
Referring to FIG. 15A, an ideal sub-pixel structure will be described. Two sub-pixels 400 and 500 are disposed neighboring to each other in a first direction x. Lenses 1 as a light-ray control modules are disposed at positions corresponding to the sub-pixels 400, 500 along the first direction x repeatedly. Due to such structure, the first direction x coincides with the light-ray separating direction. Note that shapes of optical aperture parts 410, 510 or the two sub-pixels 400, 500 are considered to be roughly in a parallelogram form for convenience sake in terms of explanation.
First, considered is a case where the aperture part 410 is divided into two sections in the first direction x. In a certain section along the first direction x, the aperture part 410 overlaps with the aperture part 510 in a second direction y. Such section is referred to as an overlapping section 401L. Further, in the other section along the first direction x, the aperture part 410 does not overlap with the aperture part 510 in the second direction y. Such section is referred to as an aperture width constant section 403.
Accordingly, the shape of the aperture part 410 is also considered by dividing it into two regions along the first direction x. Out of the aperture part 410, a region belonging to the overlapping section 401L is referred to as an overlapping region 421L, while a region belonging to the aperture width constant section 403 is referred to as an aperture width constant region 423. This can be considered the same in the case of the neighboring aperture part 510. Out of the aperture part 510, a region belonging to an overlapping section 501R is referred to as an overlapping region 521R, while a region belonging to an aperture width constant section 503 is referred to as an aperture width constant region 523. Note that the overlapping sections are the sections regulated by overlap of the aperture parts 410 and 510 in the second direction y, so that the positions of the overlapping sections 401L and 501R in the first direction x coincide with each other.
Now, the width of the second direction y out of the widths of the aperture part is defined as “longitudinal aperture width”. The longitudinal aperture widths 413, 513 of the aperture width constant regions 423, 523 are constant regardless of the positions in the first direction x. In the meantime, the longitudinal aperture widths 411L, 511R in the overlapping sections 401L, 501R vary according to the positions in the first direction x.
Further, at the same position in the first direction x within the overlapping sections 401L and 501R, the value of “411L+511R” that is the sum of the longitudinal aperture widths 411L and 511R (referred to as “sum of longitudinal aperture widths” hereinafter) is constant. Further, the sum of the longitudinal aperture widths “411L+511R” and the longitudinal aperture width 413 as well as the longitudinal aperture width 513 take the same values with each other.
Next, let's look into the total value of the longitudinal aperture widths of a sub-pixel group arranged in the first direction among the sub-pixels arranged in matrix on a display panel. FIG. 15B is a graph showing, with a plot 002, the relation between the positions in the first direction and the total value of the longitudinal aperture widths in the ideal sub-pixel structure shown in FIG. 15A. Note here that the total value of the longitudinal aperture widths is the sum of the two longitudinal aperture widths “411L+511W” in the overlapping sections 401L and 501R. It is the value of the longitudinal aperture width 413 in the aperture width constant section 403, while it is the value of the longitudinal aperture width 513 in the aperture width constant section 503.
As described above, the sum of the longitudinal aperture widths “411L+511W”, the longitudinal aperture width 413, and the longitudinal aperture width 513 take the same values with each other, so that the plot 002 is always constant for the positions in the first direction x. Thereby, generation of 3D moiré in the light-ray separating direction is to be suppressed.
Incidentally, there are various elements for constituting the optical aperture shapes of actual sub-pixels depending on the types of the electro-optical elements. Examples thereof are a black matrix, signal wirings, and the like in a liquid crystal display, partition walls, display electrodes and the like in a plasma display, a light emission layer region, signal wirings, and the like in an organic EL display. Each of those elements is manufactured by using a photolithography technique in general. Thus, the precision of those shapes depends on the pattern precision of the photolithography technique.
Considering the currently used typical materials and manufacturing devices for photolithography, it is difficult to completely eliminate processing variation of about several μm as the shape precision. Further, in order to control the processing variation to be less than the order of sub-μm level, expensive materials and manufacturing devices are required. Thus, it is difficult to provide inexpensive stereoscopic display devices. There is not a little shape dependency existing in the processing variation. Especially, the processing precision variation of a bent shape including an acute angle is relatively large. Due to the processing precision variation, fluctuation may be generated in the quality of the acquired products, e.g., the corner of the optical aperture part of the sub-pixel may be rounded, the optical aperture part may become small or large as a whole, and the like.
FIG. 16A is an explanatory chart showing changes in the longitudinal aperture width when the corner of the aperture part is rounded with respect to the ideal sub-pixel structure shown in FIG. 15A. The ideal sub-pixel aperture parts 410, 510 and the aperture parts 410a, 510a of the sub-pixels 400a, 500a having rounded corners P, Q are illustrated in a corresponding manner.
The overlapping sections 401aL, 501aR of the aperture parts 410a, 510a having the rounded corners P, Q become smaller than the overlapping sections of the ideal aperture parts 410, 510. Further, because of this change, an aperture width fluctuating section 402aL appears between the overlapping section 401aL and the aperture width constant section 403a, and an aperture width fluctuating section 502aR appears between the overlapping section 501aR and the aperture width constant section 503a. Those aperture width fluctuating sections 402aL, 502aR are generated when the parts to become overlapping sections with the ideal aperture parts 410, 510 come to have the rounded corners P, Q due to the processing precision variation so that the aperture parts do not exist in those sections.
FIG. 16B shows the results acquired by paying attention to the positions in the first direction and the total values of the longitudinal aperture widths of the sub-pixel group arranged in the first direction in such case. That is, FIG. 16B is a graph showing the relation between the positions in the first direction and the total values of the longitudinal aperture widths regarding the aperture part having the rounded corner.
As shown with a plot 002a in FIG. 16B, in accordance with the appearance of the aperture width fluctuating sections 402aL, 502aR caused by the influence of the rounded corners Q, P, positions S, T at which the value of the longitudinal aperture width radically decreases in those sections are generated locally. The value of the sum of the longitudinal aperture widths “411aL+511aR” of the other overlapping sections 401aL, 501aR and each of the values of the longitudinal aperture widths 413a, 513a of the aperture width constant sections 403a, 503a do not change since those are not affected by the rounded corners P, Q.
There are a longitudinal aperture width change value Wq and a longitudinal aperture width change section Vq at the positions S and T. The longitudinal aperture width change value Wq depends on the angle θ of a side (e.g., an aperture side 400aA, 500aB, or the like) existing in the overlapping section within the aperture part with respect to the first direction x. Further, the longitudinal aperture width change section Vq depends on the size of the rounded corners P, Q in addition to the extent of the angle θ.
FIG. 17 is a graph showing the relations regarding the angle θ of the aperture part, the longitudinal aperture width change value Wq, and the longitudinal aperture width change section Vq in a case where the corner of the aperture part is rounded.
As shown in FIG. 17, when the angle θ becomes larger, the longitudinal aperture width change value Wq becomes larger while the longitudinal aperture width change section Vq becomes smaller. Inversely, when the angle θ becomes smaller, the longitudinal aperture width change value Wq becomes smaller while the longitudinal aperture width change section Vq becomes larger. Therefore, in terms of 3D moiré, it is advantageous to have a smaller angle θ. However, when the angle θ is too small, the overlapping section of the sub-pixels becomes extremely large so that the 3D crosstalk property tends to be deteriorated.
Further, in a case where the sub-pixel size and the layout pitch are designed to be small in accordance with the recent tendency of ultra-high definition, the angle θ also becomes large. Thus, 3D moiré is deteriorated as described above. Therefore, with the ideal sub-pixel structure shown in FIG. 15A, it is essential to deal with such issue.
FIG. 18 is a chart showing 3D moiré generated when the value of the longitudinal aperture width is decreased radically due to rounding of the corner shown in FIG. 16B by using the relation between the observer and stereopsis regions. The lateral axis of FIG. 18 shows the observing angles in the first direction, and the longitudinal axis shows the luminance distribution with respect to the observing angles. The two kinds of dotted lines show the luminance distributions when an image is outputted only to either one of the pixels, assuming that a sub-pixel 400a is a right-eye pixel and a sub-pixel 500a is a left-eye pixel. That is, Y1 is the luminance distribution when white is displayed on the right-eye pixel and black is displayed on the left-eye pixel, Y2 is the luminance distribution when black is displayed on the right-eye pixel and white is displayed on the left-eye pixel, and Y3 is the luminance distribution when white is displayed on the both pixels. Basically, the relation regarding the luminance can be expressed as Y3=Y1+Y2.
Note here that a right-eye observing region is 800R, and a left-eye observing region is 800L. As shown in FIG. 18, in a case where the both eyes of the observer are located at the centers of each of the observing regions, the observer does not recognize 3D moiré. However, in a case where the both eyes of the observer are located in the vicinity of the borders (e.g., positions T, S) of each of the observing regions, the observer recognizes the radical luminance change and thereby perceives 3D moiré.
Note that the 3D moiré is called herein as black moiré when the image luminance is radically decreased. Inversely, it is called herein as white moiré when the image luminance is increased. FIG. 18 is a case where black moiré is generated.
When the ideal pixel shape shown in the related techniques is applied to the actual display panel, 3D moiré is to be visually recognized due to a steep luminance difference generated according to shift in the observing position caused by variation in the processing precision. As a countermeasure for that, it is considered to achieve an ideal shape by adding a correction pattern to the acute angle part, for example. However, in that case, even when the correction pattern is added, the processing precision variation cannot be absorbed sufficiently. Not only that, there still remains such an issue that the correction pattern itself cannot be disposed or that the correction pattern cannot function when high definition is advanced.
As a countermeasure for 3D moiré, considered is a method with which the luminance increase/decrease is eased by employing defocus of a lens. When employing defocusing, the distance from the lens vertex to the sub-pixel (referred to as “lens-pixel distance” hereinafter) is changed with respect to the focal distance of the lens to “blur” the steep luminance difference for improving the 3D moiré. However, this means to shift the focal distance intentionally, so that the stereoscopic display property typically 3D crosstalk is worsened.
Further, when using defocusing, it is important to keep the lens-pixel distance constant with high precision. When variation in the lens-pixel distance is large, defocusing is worsened further so that the 3D crosstalk property is deteriorated greatly. The 3D crosstalk herein means a phenomenon where a certain viewpoint image is mixed into another viewpoint image and displayed when performing stereoscopic display. In order to keep the lens-pixel distance constant with high precision, high processing precision is required not only for the lens manufacturing technique but also for the display panel manufacturing technique.
In a display panel where sub-pixels of narrow pitch are disposed in matrix for achieving higher definition, variation in the processing precision becomes relatively larger. Thereby, the change in the longitudinal aperture width becomes still greater. Further, the number of the sub-pixels in the display region of the display panel having a large number of pixels becomes relatively greater, so that it is necessary to keep the processing precision over a wide range of the display panel.
It is therefore an exemplary object of the present invention to provide a naked-eye type stereoscopic display device which can achieve a fine stereoscopic display property while achieving high-definition display and high yield.